What is a healthy soil?
Note Number: AG1056
Updated: September 2006
Agriculture relies on healthy soils to produce quality crops and pastures. But mention soil health and most people focus on soil fertility. There are many aspects that need to be considered when thinking about the "health" of a paddock.
Soil must be physically, nutritionally and biologically balanced be productive and stable. Soil structure decline, soil acidification and soil erosion are common soil health issues with the potential to severely restrict agricultural productivity on susceptible soil types, while erosion may also contribute to downstream sedimentation and turbidity within water storages.
Good soil health is about creating a robust soil that can withstand impacts, such as agriculture, without loss of fertility, structure and biological activity.
Victoria: the state of our soils
Many soil health problems occur as a result of natural processes, however agricultural practices can influence soil health.
- Clearing of native vegetation has changed the water balance in our soils and has removed vital groundcover.
- Severe soil acidity (pH less than 4.5) has affected soils.
- Lack of surface vegetation had led to moderate to severe gully erosion.
- Dryland salinity affects agricultural soils.
- Severe soil structural decline (hardpans, surface crusting, sodicity and slaking) affects agricultural soils.
The components of soil
Understanding and managing our soils is a vital step in ensuring the long-term sustainability of agriculture. It is important to understand that soil health issues are interrelated and are difficult to treat as single issues. With this in mind, it is important to manage soils in relation to their physical, chemical and biological properties.
|Physical features||Chemical features||Biological features|
|Structure||Salinity||Macro fauna (worms, arthropods)|
|Water infiltration & drainage||Sodicity||Soil bacteria. e.g. rhizobia|
|Topsoil structure||Total nitrogen||Fungal hyphae|
|Soil colour||Total phosphorus||Micro fauna (nematodes, protozoa)|
|Slaking||Trace elements||Abundance of roots|
The physical, chemical and biological features of soil interact and need to be managed with this in mind. For example, soil's with a low pH (less than pH 5) result in chemical imbalances such as aluminium toxicity and deficiencies of phosphorus and trace elements such as calcium and molybdenum. Very low pH (less than pH 4) leads to soil physical breakdown where the clay structure of the soil is broken down. Acid soils also impact on soil biota, reducing earthworm numbers and making Rhizobia less effective.
How do we improve our soils?
By paying attention to soil physical, chemical and biological features, soil health problems can be managed.
There are a number of practices that can be adopted into the farming system to ensure that soil continues to be productive and sustainable:
Managing acid soils:
- Apply lime once pH drops below 5. Lime is the only way to reverse acidification! Lime will create a more favourable environment for soil biota.
- Retain and sow deep-rooted perennial grasses to reduce nitrate leaching.
- Apply maintenance dressings of lime as required, after the first remedial rate has been applied (approximately 150-200 kg lime/ha/year is needed to balance the acidification caused by agriculture).
- Match timing of fertiliser application with maximum demand by plants to reduce nitrate leaching.
Managing soil erosion and run-off:
- Slow or retard water flow to reduce erosion.
- Maintain groundcover through good grazing management and retaining stubble.
- Maintain and improve drainage line vegetation.
- Adopt land class fencing and whole farm planning practices to use land within its capability.
- Minimise soil disturbance.
- Repair active gullies early.
Improving soil structure:
- Adopt good grazing practices: pay attention to stocking rates, remove livestock from wet areas, maintain vegetation cover.
- Adopt minimum tillage and direct drilling to improve soil physical conditions. Avoid cultivation if soil is too dry or too wet.
- Include a pasture phase to improve soil structure. This will improve physical soil features such as water infiltration and will increase organic matter to support greater numbers of earthworms and microbes.
- Retain stubble: to increase organic matter and improve water infiltration.
Improving soil biota:
- Use appropriate cropping rotations for improved organic matter, disease breaks and more diverse nutrient sources for soil biota.
- Maintain soil fertility: soil test regularly and apply fertilisers according to crop and paddock needs.
- Retain stubble: improves soil organic matter (food source for soil organisms).
- Minimise cultivation: retains a food source for soil biota.
- Lime acidic soils: provides a more favourable pH for soil microbes and earthworms.
- Reduce compaction: limit traffic from machinery and over-stocking. Compaction reduces soil drainage, causing unfavourable soil conditions for biota.
This Information Note was developed by Carole Hollier, Rutherglen. September 2006.
It was reviewed by Carole Hollier, Rutherglen. September 2003.